Charge forming device



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F. E. AsELfrlNE' CHARGE Fpmma DVIGE med Jan. 29, 1952 .5 sheets-sheet 5 rately to the combustion chamber itself.

Anvengine and charge forming device of UNITED STATES PATENT loEiFIcE CHARGE FORMING DEVICE Frede.

mesne assignments, to General Aseltina Dayton, Ohio, assigner, by

Motors' Corporation, Detroit, Mich., a corporatlonof 'Dela- Ware Application January 29,1932, Serial No. 589,611

17 Claims.

This invention relates to internalcombustion engines and means for supplying the lfuel charge thereto, and more particularly to an engine and means for supplying a rich mixture and air sepageneral chara this eter are shown in the copending application o f Fred E. Aseltine, Serial No. 417,087, filed December 28, i929, and the present invention ,in an aspect relates to an improved form of a construction cation.

It is an obj vdevice of the simple construction and in which a single intake which is broadly old in said appliect of this invention to provide a character described which is of valve is employed to control the admission, both of the rich fuel mixture and the air which is to be mixed therewith, to the combustion chamber.

While this invention is most particularly adapted to a charge lforming device such as 'shown in the aforesaid application in which a plurality of primary mixing chambers are provided each one of which is associated specically with one of the engine intake parts and is intended to sup- Ply a primary mixture to the cylinder or cylinders which are in communication with that prticular part. It will be understood that the invention is applicable to other forms of charge forming-devices one of which is disclosed inthe modified form which is very that shown in of the invention illustrated herein, similar in general construction to applicants earlier copending application Serial No. 362,190, filed May 8, 1929.

Further objects and advantages of the present i invention will be apparent from the following description, reference being had to the accompanying drawings wherein a preferred embodiment of one clearly shown.

form'of the present invention is In the drawings: Fig. 1 is a plan view of an engine and charge forming device constructed according to the present invention. v

Fig."2 is a v ertical section through'the charge forming `device and the upper portion of the engine block.

Figs. 3 and 4" are enlarged detailed views of the primary mixture inlets.

Figs. 5 to l0 inclusive,

of the inventi show a modied form on, and Figs. 5, 6 and '7 show reinvention.

Fig. 8 lis a view showing the carburetor unit (Cl. 12S-119) Referring to Figs. l to 44inclusive, the engine 10 disclosed in the drawings is,'with the exception of the construction of v'the intake valves and passages leading from the intake ports to the combustion chambers, of theconventional valve-inthe-head type, the engine block being indicated 15 in its entirety by the reference numeral III. The engine block comprises aplu-rality of cylinders I2 and a cylinder head I4 is secured tothe block in the conventional manner and vhas combustion chambers I6 formed therein. .Each cylinder is 20 provided with an exhaust port, which is not shown herein forthe sake `of simplicity of disc1osure, and van intake port I8, controlled by a valve indicated in its entirety-by the reference numeral 20 and more fully described hereinafter. 25 A spark'plug 22 is associated with each cylinder to ignite the chargetherein. All of the details of construction of the engine are of the usual design found in engines of this type with the exception of the passages for supplying the 30 charge to the combustion chamber andthe valves which control the admission of the charge, these details having been modied in the manner herefsage 24, under certainA operatingconditions, 45

which underother conditions the primary mixture alone is supplied to the combustion chamber. YThe passage 24 is the ordinary intake passage such as employed in the conventional form of engine'andthe passage 26 comprises a sheet 50 metal tube extending through the passage 24 horizontally and connecting at its inner vend with a horizontal tube 28 arranged at right Vangles to the tubezi and' communicating at its ends with two largervertical sheet metal tubes 30, which 5F at their upper ends are spread outwardly as in- -dicated at 32 in Fig. 2. The various sheet metal that the primary mixture tube 26 supplies two adjacent cylinders with the rich primary mixture when -the cylinder head is provided with Siamese ports, as indicated in the accompanying drawings.

Each tube 30 extends downwardly to a position a little'above the outlet of the intake passage -|8 and is normally closed by a valve surface 34 formed on the intake valve 20 which 'is provided with another valve surface 36, which closes the outer passage 24. It will thus be clear that the i single valve element 20 is provided with two separate valve surfaces which control the admission of the primary mixture and air to be mixed therewith to the combustion chamber.

The. stems 38 of the intake valves are guided in valve guides 40 positioned in the cylinder head casting and are normally held closed by springs 42 and 44 received between a collar 46 on the end of the valve stem and the casting of the cylinder head. A

The valves are adapted to be opened by a valve operating mechanism of the same construction as is normally employed vin a valve-in-the-head engine. This valve operating mechanism includes push rods 48. which are reciprocated vertically by the cam shaft (not shown) in the usual manner. `Each of the push rods operates a rocker arm pivotally mounted on a shaft 52 supported in standards 54 extending upwardly from the cylinder head from the. cylinder head casting. The rocker arms are each provided with means indicated at 56 for adjusting the clearance between the push rod and the rocker arm in the usual manner, while the opposite end of the rocker arml is provided with a projecting surface 58 engaging the upper e'nd of the valve stem 38 and on upward movement of the push rods 48 pushes the associated valve stem downwardly to open the valve and admit the separate portions of the charge to the combustion chamber through the passages 24 and 26. The valve operating mecha- 'nism is covered by sheet metal housing 60 of the type usually employed with engines 'of this character.

Associated with the above described engine Vhead is an intake manifold indicated in its entirety by the reference character 62 and having three outlet branches 64, 66 and 68, each of 'which registers with one of the intake ports 28 when the device is assembled. 'I'he manifold is adapted to Vbe secured to the engine-block in the 'conventional manner and when assembled, the

fNo. 370,179. "Tight fitting metal collars I2 surround the conduit 'I0 and the tubes 26 at theiradjacent ends to prevent leakage. The outlet branches of thei manifold are all supplied with air through a common inlet 14, which communicates with the secondary air passage in' a main corresponds to a vehicular speed oiapproximately 15.to 20V-miles per hour and at speeds above this,

carburetor unit adapted to be secured to a flange Y 'I6 at the" manifold inlet.

The .carburetor unit, sueltas shown in the drawings, .is-,of substantially the same construction as that which is fully described in the ap- 370,179, above referred to, and need not be described'in detail herein, it being suicient for i ofthe main housing and has certain fuel supply lpassages and other elements of the carburetor formed therein. A sheet metal fuel bowl is held tight against a flat surface on the main housingl by the screw 86 screwed into the casting 84 and fuel is conducted froml a main source of supply to the fuel bowl where a substantially constant level of fuel is maintained in the usual manner.

' Fuel is supplied from the fuel bowlV to a plurality of mixture passages 88, which register with the conduits 10 by means of nozzles 9D, whichextend into chambers 92 where the fuel issuing from the nozzles is mixed with a smallamount of air, this mixture or emulsion, being 'supplied to the passages 88 through orifices S4. The fuel supply passages are not shown, nor is but one of the primary mixture passages 88 and the associated chambers 92. There are, however, three of the passages 88 and three of the chambers 92 communicating therewith, while a nozzle 90 projects into each of said chambers.

' sage I I4 is rendered effective to supply air to the manifold and thus to the passages 24, but during all operation when thethrottle has/not been opened to the position referred to, theH primary mixture is of combustible proportions and is all that is supplied to the combustion chambers.

Air is admittedthrough Ythe coupling 82 and is controlled by a valve I 89 normally held closed .by a spring |82; received between the valve and ange The primary mixture Ypassages supply allof the fuel mixture during A |04, projecting from a sleevej' which is slidable on a fixed sleeve |08, which guides the stem of the air valve. In order to choke the carburetor to facilitate vstartingfthe valve is manually held closed by means not shown herein but,

fully described in application No. 370,179.

' The valvev |80 admits air: to ia main air chamber ||0 from which passes through an opening ||2 to the chambers 92'to be mixed with fuel.

therein as previously described and also to the manifold' inlet through a' secondary air passage I4, as 'shown in Fig. 2. Ihe'ilow of air through the passage `||4 is controlled by.manually and suction operated valves `||6 and |`|8 secured to shafts |20l andl |22 respectively, the valve H6 --being opemtedby the primary throttle 96 through the medium of an operating connection which is designed -toallow the primary throttle to be moved to a'predetermined position before the valve IIS begins to open as vhereinbefore'; described. This predetermined positionof the throttle is one which air is alsosiipplid through the passage H4, the

the primary fuel' mixture The valve I8 is operated entirely by engine suction and its opening movementlis retarded to some extent to aid in securing satisfactory operation during the acceleration period, the means for controlling this valve being fully described in applicationSerial No. 370,179. It is believed to be unnecessary to describe the structure of theA carburetor unit in greaterdetail as the improvement which comprises the present invention can be fully the passages 24 and on opening movement of such valve, permits the primary mixture to enter the combustion chamber-and if the throttle has opened beyond a .predetermined position, the

valve also admits air through the passage A24 to the combustion chamber, the mixture of air with the-primary mixture taking place in the combustion chamber' itself. The principle of operation of this device is much the same as that disclosed in the ccpending application Serial No. 417,087 and the same beneficial results are secured theref by but this device has been simplified by the elimination. of a separate intake valve to control the admission of the primary mixture and the valve operating mechanism for operating the additional'valve, in this device a single valve performing thel work of two valves which were disclosed inthe application referred to.

One of the desirable results referred to above is superiorfuel distribution. Bymeans of this device no vprimary mixture tube other than one which is associated with a'cyiinder in which the piston `is on its suction -strokecan deliver any vfuel as this is the only primary tube which is subjected to enginev suction. 'I'here is therefore f no possibility of puddling of fuel in the manifold outlet branches or the intake passages formed within the cylinder head. 1

`Further by delivering the primary mixture close to the spark plugs" and effecting the mixing of air with said primary mixture in the combustion chamber it is possibleto operate the engine on av leaner mixture than is possible when other charge forming devices are used, resulting in considerable fuel saving..

It is also found l ingthe acceleration period is improved because when the primary mixture tubes deliver directlyv O. to the combustion chambers the variations in velocity of ow through such tubes is minimized, and following opening movements of the' throttle there is/les's dilution of the mixture by admission of auxiliary air during the acceleration period.

. In the modified form lof the invention disclosed in Figs. 5 to 11 inclusive, the construction of the cylinder block and valve mechanism controllingthe passagesI therethrough vis substantially the same as in the form of the invention previously described,v but the carburetor unit and manifold are of modified and only one primary 'carburetive device is employed, which supplies fuel to all of the engine cylinders. The carburetor unit is of substantially the same form as that shown inr application-Serial No. 362,190, iiled May 11,- 1929,

that the engine roperation durand will be only briefly described herein except insofar as the earlier device is little changed.

'Ihe carburetor unit comprises'a casing indicated in its entirety by the reference numeral |20 and comprising a fuel reservoir |22 to which fuel'is supplied from a main source of supply through a passage |24 controlled by a valve |26 operated bya oat |28 to maintain a substantially constant level of fuelin the fuel reservoir in the usual manner.' i

The carburetor unit is secured by flanges |30 i and |32 to the manifoldin the conventional manner, and is provided with a main air passage |34 therethrough, having an air inlet |36 controlled by a suction operatedair valve in a manner laterv described and an air outlet |38 which registers with acorresponding passage |40 in the manifold as shown in Fig. 8. A primary air inlet |42 is provided which admits air. to a primary air chamber |44 from which it flows into a primary mixing chamber where it is mixed with fuel to form a primary mixture of fuel and-air which i: conveyed through primary mixture passages .|40 and |48 in the carburetor and manifold respectively, to be mixed with air supplied through the passage |34 under certain conditions as hereinafter set forth. l

The construction of the primary mixing chamber and means for supplying fuel thereto is substantially the same as in application Serial No.

362,190, the mixing chamber being formed within a sleeve which i.; positionedin a centrally de-V pending portion |50 of the top |52 of the main fuel reservoir, as shown in Fig. 5 and more fully described later. Projecting downwardly therefrom into the fuel inthe reservoir' is a fuel ponduit |54 having a metering plug |55`screwed into its lower end, which regulates the supply of fuel. Screwed into theY upper endof the conduit |54 is a fuel supply tube |58 having a plurality of fuel feeding orifices |00 adapted to be rendered effective to supply fuel successively, as the suction in the primarymixing chamber increases. Air

is supplied -to the primary mixing chamber through the above described primary air inlet |42, the size of which may be regulated asdesired by means of a valvel operated by an operating handle |64 projecting from thevalve, while-air may also be supplied to the primary mixing chamber throughA the passage 66 which connects the main air passage with the primary4 mixing chamber, but it will be undrstood`that this air inlet may be omitted if desired, and all of the air for the primary mixture may be taken through the passage' |42 or tube' |50.

` Formed integrally `with the valve |62 and operating lever |64 .is a sleeve |68 which projects downwardly into the depending portion of the float chamber top and i n which the primary mixing. chamber |50 is formed. In the wallof the sleeve |68 are portsv |12 and |14 which are adapted to register with Ile-and"|18communicating with the primary mixture passage |46 below and above the throttle therein respectively, as the sleeve .is` rotated to different positionz A suitable operating connection is adapted to extend4 from the operating lever |54 tol a point con'- venient to the operator of the vehicle, so that the 1 sleeve |68 may be adjusted manually. The construction of the primary mixingchamber and associated parts of the device 'is'just the sarneas in application Serial No. 362,190except in two particulars, so that it will not be more minutly described herein, as it is believed that a description of thev operation of the device is all that is necessary to enable a clear understanding to be had. 'I'hev two'points of difference between the present showing and the earlier device are the following. vIn the earlier device the air inlet passage |66 is omitted and the passages |16 and |18 connect directly with the passage |34 which is the main mixture passage instead of connecting withl a primary mixture conduit such as the passage |46 in this device. The operation is substantially the same as in the earlier case. Manual adjustment of the valve |62 and sleeve |68, not only controls the size of the air inlet supplying air to the primary mixing chamber,'but also by control of the passages |16 and |18 regulates-the degree of suction communicated to the said mixing chamber so that substantially any desired mixture proportions may be secured. The sleeve |68 is adapted to be moved s0 that the passage |42 is nearly closed and the passage |18 connecting with the primary mixture passage above the throttleV is open, when it is desiredto start the engine or when operating at idling or very low speed while at other times the sleeve is moved to adjust the area of the passages |42, |16 and |18 as desired.

i It will be understood that the device may be con'str-ucted with the ports |12 and |14v in such position that both passages |16 and |18 may be partly open at the same time, or such ports may be so positioned that before either one of such passages begins to lopen. the other is Yfully closed, the first .mentioned construction being deemed preferable. l

. Admission of air to the main air passage |34 is controlled by a pivoted valve |80, theopening of which is controlled by a dash pot comprising a piston |82 sliding in a cylinder |84 and pivotally connected to the valve by a rod |86. A spring |88 within the dash pot cylinder normally lifts the pistonv to hold the valve closed, the structure of valve and dash pot being substantially the same as in application 362,190. 1

As has been stated previously the primary mix- 1 ture in this device is not delivered directly to the passage |34 as in the device disclosed in the earlier application, but instead the passage |416 communicates Vwith the vertical passage |48 which is cast in the manifold as shown herein or may bcformed separately if desired. `This horizontal passage and |86 which register with corresponding passages |98, 200 and 202. formed in theengine cylinder head, one of which is shown in detail in Fig. 11. 4Each of the passages 200, 202 and 204- is adapted to supplytwo adjacent cylinders of the engine as shown in Fig. 11 and to this end said passages connect with horizontal passages 206,208 and 2|0 respectively, while each of the latter passages connects with two of thevertical passages 2|2, the lower end of each of which forms a seat for a beveled surface 2|4 formed on 'the engine intake valve, which in -closed position entirely closes the primary mixture passage 2|2 associated therewith.

The riser |40 of the air manifold connects at its upper end with a horizontal passage 2|6 which communicates with three outlet branches 2|8 formed in the manifold casting below the primary mixture passages |92, |94 and |96, all ofl these outlet branches being of the same construction and one of'said branches being shown in detail in Fig. 8. Each of the branches 2|8 communicates with a horizontal passage 220 communicating with two downwardly extending primary mixture and air and when the throttle l valve of the carburetor air passage is open, the

` mixture of air with the primary mixture is effected in the combustion chamber of the engine cylinder itself.

The control mechanism for controlling the quantity of mixture supplied to vthe engine and the proportions of fuel and air therein is somcwhat different from that disclosed 'inapplication Serial No. 362,190, and this mechanism will, therefore, be briefly described. In the earlier device there is only one throttle in the passage corresponding to passage |34 of this application and such throttle is manually operated. In the present structure the passage |34 is controlled by twovvalves 230 and 232, the rst being manually operable by a lost motion connection operated from a primary throttle 234 in the passage |46, while the valve 232 is operated wholly by suction which is effective thereon after the valve 238 has begun to open. The primary throttle is fixed to a spindle 236 journalled in the casing and secured to the end of thespindle' outside the casing is an operating'arm 238 having an orifice 240 in which some operating connection extending to the dash of the vehicle is adapted to be connected. Pivotally connected tothe arm 238 is an operating link 242, the` other'end of which is received in a slot 244 formed in a plate 246, secured to a spindle 248 journalled in the housing and on which the air throttle 230 is secured. A spring 250 connected in a very suit- -able way to said plate 246 and the housing normally holds the throttle 230 in closedposition. As the arm 236 is moved in countercloclrwise direction to open the primary throttle the latter is opened independently of the throttle 23|!Y until the link 242. engages the left end of slot 244 after which both .throttles are moved together. The primary throttle is generally designed to open to a position corresponding to a vehicular speed of substantially 15-20 miles Der hour on a level .i

before the throttle 230 begins to open. However,

the connections may be varied to .permit any amount of independent movement of the primary throttle which maybe desired., f.

'I'he plate 246 is provided with a slot 252 which cooperates with a'hole 254 in the housing to admit air-at intermediate speeds Iona. purpose set forth and forming no part of invention.

- The suction operated valve`232 is secured to a shaft 256 journalled in the-housing. and-'the shaft has secured at one end thereof an arm258 to which is pi-votallyI connected apiston rod 260 which operates the piston 262 of a.- combined dash;

pot and fuel pump which need not be specically described as it forms no part of thelpresent' in-f vention but is fully described in the earlier ap-l plication. 1

It will be clear lfrom the foregoingdescription that on the modified form ofthe invention subtained at all times in the primary mixture passage, preventing accumulation of fuel on the walls thereof as would occur on the manifold walls if a conventional type of carburetor were employed. vOther advantages mentioned in connection with the preferred form of the invention are also secured. V

While the form of embodiment of the present invention as herein disc'losed, constitutes a preferred form,` it is to be understood that other forms might be adopted, all coming within the scope of the claims which follow.

What is claimed is as follows:

l. In combinationwith a` multicylinder engine having a plurality of separate passages formed therein to convey separate charges of fuel mixture and air to each cylinder, a. charge forming device comprising a carburetor having a plurality of primary mixing chambers in which a primary mixture of air and fuel is formed, a

secondary air passage in said carburetor unit, a plurality of conduits connecting each one of the primary mixing chamber with one of the fuel mixture passages in the engine, an air conduit connecting the secondary air passage with all of the air passages in the engine and a single valve controlling the fuel mixture `and air vrpas- 1 sages associated with each cylinder.' y

2. In combination with a multicylinder engine having a plurality of separate passages formed thereinto convey separate charges of fuel mixture and air to each cylinder, a charge forming device comprising a carburetor unit vhaving a single primary mixing chamber onwhich a primary mixture of air and fuel is formed, a secondary air passage in said carburetor unit, a branched primary mixture conduit which connects the primary mixing chamber with all of the fuel mixture passages inthe engine and an air conduit connecting the secondary air passage with all of the air passages in said engine.

y3.A In combination with a. multicylinder `en gine having a plurality of separate passages formed therein to convey separate charges of fuel mixture Vand a'ir to each cylinder, a charge forming device comprising a carburetor unit having 4.- In combination with a multicylinder internal ,combustion engine having separate passages formed therein to convey separate charges of fuel mixture and air to each cylinder. a ,charge forming device comprising a carburetor unit having a plurality of primary mixture passagesI in which a primary mixture of air and fuel is formed, a secondaryv air passage therein, a manifold having a plurality of vprimary mixture conduits therein connecting each of the primary mixture passages with one of the fuel mixture passages in the engine and an air conduit connecting the-secondary air passage with all of the'air passages .formed in the enginepand'a vsingle intake valve for controlling the outlets of saidseparate passages which communicate withthev encomprising a. plurality of; primary carburetors.`

forming device for a multicylin provided with means for admittingfuel and air thereto, a plurality of passages leading from said primary carburetors to the engine intake ports.

means admitting secondary air to be mixed with said primary mixture, passages leading from air admitting means tothe engine intake ports, said last named passages being entirely separate from and having no communication with the passages from the primaryfcarburetors, and a single intake valve controlling the outlets of said air and mixture passages which communicate with an engine cylinder.

6. A charge forming device for prising a plurality oi' primary carburetors provided with means for admitting fuel and air thereto, a. plurality of passages leading from said primary carburetors totheengine intake ports, a single air inlet supplying secondary 'air to be mixed with said primary mixture, passages leading from said single air inlet to the engine intake ports, said last named passages having vvand air to each primary carburetor, a main air inlet, mixture and air,conduits extending from saidprimary carburetors and air inlet respectively, to the engine cylinders, said conduits being separate and having no communication with each other, and a single intake' valve controlling the outlets of said air and mixture passages which communicate with ank engine cylinder.v

8. A charge forming device for a multicylinder engine having a plurality of intake ports, comprising a carburetor unit having a plurality of vprimary carburetors formed therein, an air inlet passages in said carburetor unit, a manifold interposed between the carburetor and the engine intake ports,` passages in said manifold comvmunicating with the primary carburetors and air inlet passage respectively, said passages in -the manifold being separate and having no communication with each other, and a single intake valve controlling the outlets of said air and mixture passageswhich communicate with an engine cylinder. A

9. In combination, a multicylinder engine hav- .ing a plurality of intake -ports. each of which comprises a plurality of openings adapted to communicate `with separate. passages leading to the engine cylinders, a carburetor unit therefor having a mixture outlet passage and an air supply passage forined therein, a. manifold inter posedbetween the carburetor unit and th engine intake port.. said manifold having means for conveying the mixture from the carburetor unit to one of the openings at each intake port, means for conveying airA from the air supply passage to the other 'of said openings at each intake port, and a singlel intakevalve controlling the communication of said separate passages with -the engine cylinder. y

` 10. In combination, amulticylinderenginehaving a plurality of intake ports, each of which comprises a plurality of openings adapted to communicate 'with separate passages leading to the amulticylinder engine having a plurality of intake ports comengine cylinders, a carburetor lunit therefor havcontrolling the communication of said separate passages with the engine cylinder.

ll. In combination, a multi-cylinder internal combustion engine having cylinders in each of which is formed a combustion chamber, separate mixture and air ports for admitting separate charges of fuel mixture and air only to each combustion chamber, a charge forming device associated with said engine, said device having means for supplying fuel mixture to said mixture ports under all operating conditions and means for supplying air only to said air ports under` certain operating conditions, and a single intake valve for controlling both of said ports.

l2. In combination, a multi-cylinder internal combustion engine having cylinders in each of. which is formed a combustion chamber, separate mixture ports for admitting separate charges of fuel mixture and air only to each combustion chamber, a, charge lforming device associate with said engine, said device having'a primary mixing chamber and a secondary air inlet, separate conduits connecting the primary mixing chamber with-said mixture ports and the. secondary air inlet with said air ports, and a single intake valve controlling both of said ports.

13. In combination with a multi-cylinder internal combustion engine in each cylinder of which is formed a combustion chamber, separate mixture and air ports for admitting separate charges offuel mixture and air only to said y combustion chamber, a charge forming device associated with said engine and including means for supplying fuel mixture through said mixture ports under all"conditions of operation, means for supplying air to 4said air ports, and means for controlling the supply of air so constructed that airis not supplied to said air ports at low engine speeds, anda single intake valve for controlling the separate ports which communicate with the combustion chamber.

414. 1n combination with a multi-cylinder internal combustion engine having separate passages formed therein to convey separate charges of fuel mixture and air to each combustion chamber, a charge forming device associated therewith including a carburetor unit having a primary mixing chamber formed therein, means for supplying fuel and air thereto to form a primary fuel mixture, an auxiliary air inlet in said carburetor unit,-separate conduits for conveying the fuel mixture and air from the primary mixing chamber and said air inlet .to said separate pasi sages, so constructed that one of said conduits conveys air only and the other fuel mixture, means for controlling the now through said conduits, said means being Vconstructed to prevent a i' trolling the communication of said separate passages with the combustion chamber.

15. In' combination with a multi-cylinder internal combustion engine having separate passages formed therein to convey separate charges of fuel mixture and air to each combustion chamber, a charge forming device associated therewith including a carburetor unit having a primary mixing chamberforrned therein, means for supplying'fuel and air thereto lto form a primary fuel mixture, an auxiliary air inlet in said carburetor unit, separate conduits for conveying fuel mixture and air from the primary mixing chamber and said air inlet to said separate passages, so constructed that one of said conduits conveys air only and the other fuel mixture, a primary throttle for controlling the flow of fuel mixture through one of said conduits, a secondary throttle operated thereby for controlling the flow of air through the other of` said conduits and constructed to begin its opening movement after the primary throttle is partly opened, and a single intake valve controlling the communication of said separate passages with the combustion chamber.

16. In combination with a multi-cylinder internal combustion engine having separate passages formed therein to convey separate charges of fuel mixture and air to each combustion chamber, a charge forming device associated therewith including a carburetor unit having a primary mixing chamber formed therein, means for supplying fuel and air thereto to form a primary fuel mixture, an auxiliary air inlet in said carburetor unit, separate conduits for conveying fuel mixture and air from the primary mixing chamber and said air inlet to said` separate. passages, so

vconstructed that one of said conduits conveys air only and the other fuel mixture, a primary throttle for controlling the flow of fuel mixture through one of said conduits, a secondary throttle for controlling the flow of air through the other of said conduits, means for 'operating said throttles concurrently, and a single intake valve controlling ture, an auxiliary air inlet in saidgcarburetor unit, separate conduits for conveying fuel e and air from the primary mixing chamber `and said air inlet to said separate passages, so constructed that one of said conduits conveys air only and d i the other fuel-mixture, a primary throttleV for.

controlling the now of mixture through one of said conduits,-a suction operated valve controlling the flow of air through the other of said conduits,

means for temporarily retarding the opening of Y said valve during the acceleration period following opening movement of the throttle, and a'single intake valve controlling -the communication of said -separate passages with the combustion chamber. 

